Manufacture of phenyl esters of phosphoric acid



Patented Oct. 17, 1933.

mesne MANUFACTURE-F PHENYL ESTERS fPHOSlfl-IORICACID-q ,7 I,

EriIiCIeinmenSeTnJSt. Louig Mm, assigrior, 'byf signnients, to 'Mo'nsz'ilnto Chemical .t ren a,.cri rrap'ration of pelawa g No? Drawing. Application September 29. 19 in V 1 SeriaLNo.485,311,

This invention deals with the adaptation-it: phosphate esters such as phenyl phosphates and thio phosphates according-to"which thecrude ester is treated, preferably in the presence of an aqueous medium, witha-small quantity of a permanganate whereby the color and odor imparting impurities are destroyed without decomposi thiophosphate, tritolylthiophosphate, as well as the corresponding alkyl and the, mixed alkyl alphyl esters, are used extensively in the manufacture of nitrocellulose and acetyl cellulose prod- V ucts. These esters are prepared (1) by heating the alcohol, such as a phenol, with phosphorus oxychloride, (2) by causing an alkali phenate to react with phosphorus oxychloride in an aqueous medium maintained at low temperatures and (3) p} by causing phosphorus oxychloride to react in an 5 inert medium with an alkali phenate. The corresponding thiophosphoric acid esters are made in an analogous manner. The esters made by these processes invariably contain impurities which I impart color and odor to the ester and which '30 suffer decomposition in the presence of actinic ray. Inasmuch as these esters evidence a slight decomposition at or near their boiling points even under greatly reduced pressures, their purification by distillation is unsatisfactory. Various materials havebeen employedfor the purpose of destroying or removing the color, odor and light sensitive impurities, including bone-char, charcoal and other absorptive agents without com- I H plete success and generally at a substantial sacri- Crystallization from solvents such as alcohol particularly when employed in conjunction with charcoal or bone-char results in a satisfactory product, but suffers the disadvantage of costly solvents and extensive equipment. Moreover, the

necessity of reworking the mother liquor as well as of partly purified'crops of crystals and recovery of solvent renders this process both cumbersome and costly.

I have now discovered that the impurities which are light sensitive or impart color or odor to this class of phenyl esters may be completely and easily removed or destroyed by treatment with an aqueous solution of a permanganate, such as potassium permanganate.

(cream-9mg;

. 'Accordingto this invention the crudephenyl ester, which invariably is of a yellowish or. brownish hue, has a characteristic odor-and suffersgdisq coloration'lupon exposure to ultra-violet rays; is agitated with an aqueousi solutionzof a permanganate atordinaryonslightly elevated-:iifimpera v tures. After the permanganate is no longer consumed by the ester, evidencing complete removal of undesirable impurities, the excess permanganate is removed by washing with water or de- 55; stroyed by adding a small amount of a sulfite or acid sulfite thereto. Any precipitated manganese dioxide is dissolved by means of an acid, such as hydrochloric, sulfuric or sulfurous, which is washed from the product by means of water. The 7 resultingester is then dried in any convenient manner. The product so obtained is colorless, odorless, stable in the presence of actinic ray and otherwise will be suited for use in cellulose ester technology.

, Asa source of permanganate one may employ the soluble salts thereof including sodium, potassium or calcium derivatives. For the purpose of removing precipitated manganese dioxide, I prefer to employ sulfuric acid which may be removed completely and easily from the purified ester by washing with water. Obviously, the' manganese dioxide precipitate may be separated from the ester in other ways, as by filtration, if desired. 1

An example of the manner of applying the "principles of my invention to the purification of triphenyl phosphate is hereinafter set forth, it being understood that the invention is equally applicable to the refining 'and purification of 90, other esters of this class.

A suitable vessel is charged with 200 parts of crude triphenylphosphate such as results from any of the well known processes for its manufacture and is agitated at about 50 C. for sev- 5 eral hours with 800 parts of .3% of aqueous potassium permanganate. Additional permanganateshould be added if an excess as'evidenced by its color, does not persist for a period of a v half hour in the mixture containing the crude phosphate. Thereupon the excess permangae nate is removed by washing with water after which any precipitated manganese dioxide that remains is dissolved by adding sulfuric acid thereto. Subsequently, the ester is 'washed with water until it is free of acid, and afterward is dried.

What I claim is:

1. In the refining of phosphate esters, that step which consists in treating the crude phos- 1'10 phate ester with a water soluble permanganate.

2. The method of refining phosphate esters which comprises treating the crude phosphate ester with a water soluble permanganate in the presence of an aqueous medium, washing the excess permanganate'from the mixture, and dissolving precipitated manganese dioxide remaining in the ester by means of a mineral acid.

' 3. The process as defined in claim 2, wherein.

the precipitated manganese dioxide is dissolved with sulphuric acid.

4. In the refining. of phosphoric acid esters the steps which consist in treating the ester with aqueous solution of an aikalimetal permanganate and subsequently separating the ester from the aqueous solution and precipitated mangav nese dioxide.

5. In the refining of aryl estersof phosphoric acid, the steps which consist in treating the ester with an aqueous solution of an alkali metal per manganate and subsequently separating the ester from the aqueous solution and the precipitated manganese dioxide.

s. The method as defined in claim 5- and iurther characterized in that the precipitated manganese dioxide is separated by filtration.

7. In the refining ofphosphate esters that step which consists in treating the crude phosphate ester with a water soluble permanganate in'the presence of water and subsequently separating the ester from the aqueous solution.

8. In the refining of'tri-tolyl phosphate, the step which consists in treating the phosphate with an aqueous solution of a water soluble permanganate and subsequently isolating the ester from the aqueous solution. I

e. g 9. In the refining of tri-aryl phosphates wherebya, pin-e stable product is obtained without distillation thereof, the step which consists in treat-,

I ERIK CLEMMENSEN. 

